The NIH mouse potency test for rabies vaccine is a highly variably assay system. A fourth manufacturer of Rabies vaccine was licensed this year. Currently, CBER tests approximately 70% of incoming lots by the NIH mouse potency test; a laboratory based Single Radial Immunodiffusion(SRID)test is performed on non-absorbed products as a research tool. The in-vitro antibody-binding test is used for absorbed products in parallel with the NIH mouse test. We plan to continue to use SRID as a screening method with U.S. licensed rabies vaccines and explore ways to achieve better correlation between NIH and SRID tests. We also plan to investigate the potential for an ELISA type test for correlation to animal tests.